New devices that monitor and treat disorders such as cardiac or neural disorders rely upon patient interaction. Patient interaction may occur when a patient decides to adjust the operation of the implanted device, such as to turn the device on or off or to make an adjustment to its parameters. Patient interaction may also occur when the implanted device is set to relay data or an alert signal to an external device which can occur when an abnormal cardiac or neural event is detected. The patient can then interact by pressing a button on the external device to acknowledge that the alert signal has been received and that appropriate action (calling 911) will be initiated.
Internal (implanted medical device or “IMD”) and external (external device or “EXD”) components of a medical system usually communicate in two modes. In a first mode, near-field communication is used. This is a relatively low power mode in which the external and internal device are placed very close to each other (e.g. within 2-3 inches). In the case of a cardiac device, the EXD must be placed directly over the chest where the IMD resides so that information can be transmitted and received without using much power. In a second manner of communicating, a far-field mode is used. Far field communication can use an antenna of the IMD and can transmit signals over a limited distance, such as 6 feet.
In order for the IMD and EXD to communicate the external components must be within a specified range (e.g. 6 feet) so that the transmissions from the internal components can be obtained by the external components, and vice-versa. Failure of the patient to keep the EXD within this range can prevent the IMD and EXD from communicating successfully. This can be known as an “out of range (OOR) error.” Various types of OOR errors can occur in response to a number of different OOR events. These OOR events may include, for example: the IMD not finding the external device, the implantable device only finding an external device that is not the primary EXD with which it is intended to communicate, or the EXD not finding an IMD. Another type of OOR event occurs if an IMD or EXD is able to reach the sister device, but the signal is very weak, indicating that the devices may be “almost” out of range. Yet another type of OOR event occurs if one of the devices is able to reach the other device, but the communication interruptions exceed a specified criterion, indicating that the devices may possibly be “almost” out of range or that electromagnetic interference may be present.
There is a need for a system that can mitigate the problems associated with OOR events.